(1) Field of the Invention
The invention of the present application relates to a main bearing for supporting a crankshaft of an internal combustion engine.
(2) Description of Related Art
A crankshaft of an internal combustion engine is supported at a journal section thereof by a cylinder block lower part of the internal combustion engine via a main bearing made of a pair of half bearings. For the main bearing, a lubricating oil that is discharged by an oil pump is fed into a lubricating oil groove that is formed along an inner circumferential surface of the main bearing through a through-port that is formed in a wall of the main bearing from an oil gallery that is formed in a cylinder block wall. Further, a first lubricating oil path is formed by being penetrated in a diameter direction of the journal section, and both end openings of the first lubricating oil path communicate with the lubricating oil groove of the main bearing. Furthermore, a second lubricating oil path passing through a crank arm section is formed by branching from the first lubricating oil path in the journal section, and the second lubricating oil path communicates with a third lubricating oil path that is formed by being penetrated in a diameter direction of a crankpin. In this manner, the lubricating oil which is fed into the lubricating oil groove formed on the inner circumferential surface of the main bearing through the through-port from the oil gallery in the cylinder block wall passes through the first lubricating oil path, the second lubricating oil path and the third lubricating oil path, and is supplied between a sliding surface of the crankpin and a connecting rod bearing from a discharge port that is opened in a terminal end of the third lubricating oil path (for example, see JP-A-8-277831).
Conventionally, as the main bearing and the connecting rod bearing, sliding bearings each configured by a pair of half bearings have been adopted, and in each of the sliding bearings, a so-called crush relief is formed adjacently to abutment surfaces of the half bearings. A crush relief corresponds to a gap region that is formed in a space from a shaft to be supported by forming a wall thickness of a region adjacent to a circumferential end surface of a half bearing so that the wall thickness becomes thinner toward the circumferential end surface (for example, see SAE J506 (item 3.26 and item 6.4), DIN1497 (section 3.2), JIS D3102). The crush relief is formed with an objective of absorbing a positional displacement and deformation of the butting surfaces of the half bearings in a state in which a pair of half bearings are assembled (For example, see JP-A-4-219521).
Meanwhile, in recent years, in order to decrease the leakage amount of the lubricating oil from a bearing end portion in response to downsizing of a lubricating oil supplying oil pump, there are proposed a bearing in which a circumferential groove is formed by boring an inner circumferential surface of a bearing circumferential end portion, or a bearing which is configured so as not to communicate a lubricating oil groove formed along an inner circumferential surface of the bearing with a crush relief (namely, configured to form a raised portion between the lubricating oil groove and the crush relief) (see JP-A-2011-58568, and JP-A-2008-95858).